The proposed border force would include uniformed officers and officers from Special Branch.

It comes just months after the UK Border Agency was launched - comprised of officers from the Border and Immigration Agency, HM Revenue and Customs and UK visas.

At the time the Conservatives dismissed the agency as "lacking the powers to chase people traffickers and employers of illegal labour".

On the idea of a police border force, the Home Office said the Green Paper looked at a "number of proposals for policing at the border, including the Acpo proposal".

"No decision has been taken about the future of border policing and we are keen to use the Green Paper to invite wider views," a spokeswoman said.

Shadow home secretary Dominic Grieve said such a force would be "welcome but very overdue".

"For two years we have been calling for a dedicated border police force - something ministers have consistently rubbished," he said.

"Having dithered, the government have now realised their error and are trying to play catch up."

A spokesman for Acpo said it saw merit in creating a separate agency or force to work closely with the UK Border Agency.

"The government's focus should be on border control and this agency would focus on security, and would preserve the distinction between operational policing and the government."

The Home Office revealed its plans as the independent reviewer of UK terrorism legislation, Lord Carlile, warned in his annual report there was "real anxiety" among senior police officers at the potential use of light aircraft as "vehicle bombs".

He also criticised police for overusing anti-terrorism stop-and-search powers, saying their use should be halved.

'Aviation theme'

BBC home affairs correspondent Danny Shaw said aviation security has been a theme of Lord Carlile's reports.

In his latest, Lord Carlile highlights the risk of terrorists hijacking executive jets which travel at high-speed across continents.

Although there is said to be no intelligence about this, Lord Carlile said senior police officers had concerns, given the large number of private aircraft and small airfields.

Also in the report, the peer criticised police for over-using powers to stop-and search-people under the Terrorism Act - there were five occasions in 2007 when officers did not have authorisation.

He said there was an "inconsistency of approach" among chief constables about the powers.

I am satisfied that the level of arrests is proportionate to perceived risk

Lord Carlile

It emerged last December that Sussex police had wrongly deployed the measures at Gatwick airport, where they unlawfully stopped and searched hundreds of people.

Lord Carlile's document showed that similar errors were made by the Greater Manchester and South Wales forces last year.

The police must obtain ministerial authority before they designate an area a stop-and-search zone under the Terrorism Act 2000.

To remain legal, this must also be renewed regularly, otherwise the police could be sued for wrongful detention.

Lord Carlile said 12 people were detained. He hoped they had been informed of the mistake in writing, so they could consider suing the police.

The peer also said that 257 people were arrested under terrorism powers in 2007, of whom 126 were eventually released without charge.

"The realities of this kind of policing increase the possibility of arrests later found to be of innocent members of the public," he said.

But he added: "I am satisfied that the level of arrests is proportionate to perceived risk."

Lord Carlile also expressed "serious worries" about the Crown Prosecution Service's practice of charging terrorist suspects on the basis of less evidence - the so-called "threshold test".

He said it contained "at least as many and certainly more concealed risks of causing unfair extended detention" as the proposal for 42 days' detention.

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